"We like it to be realistic, but not real, so I wear something that I have called the 'vag pad,'" the actress, 24, explained during an appearance on Chelsea Lately Monday night. "It's like a little triangular, kind of, panty liner that you stick to yourself."

As for her onscreen partners, said Rossum, "The guy wears, like, a sock."

The single star -- she recently split with Counting Crows frontman Adam Duritz, 46 -- also talked sex recently with Vegas Magazine. "It doesn't make sense that the character would wear a bra and care at all about what she looks like when she's having sex," she said. "Sex is meant to feel good, and she wants to feel good."